lntest: extend the restore/restart methods to also accept optional SCBs
lntest: extend the restore/restart methods to also accept optional SCBs

In this commit, we modify the `RestoreNodeWithSeed` and `RestartNode`
methods to also accept an SCB. This will be useful in new integration
tests to properly exercise the various restore/restart scenarios using
static channel backups.

LightningNetwork/lnd,LightningNetwork/lnd,aakselrod/lnd,aakselrod/lnd